1. Field of the Invention
The present invention generally relates to an optical disk apparatus, and more particularly, to an optical disk apparatus which rotates an optical disk relative to an optical head for optically recording data on tracks formed on the optical disk or optically reproducing recorded data therefrom.
2. Description of the Related Art
An image filing system uses an optical disk apparatus which rotates an optical disk having a number of spiral or concentric tracks formed on its surface for optical data recording on the tracks or optical data reproducing therefrom.
An original is two-dimensionally scanned with light to photoelectrically convert image data of the original into electric image data, which is then optically recorded on the tracks on the optical disk by an optical head. At the time of data retrieval, the recorded data is searched and retrieved by the optical head and is reproduced as a hard copy or soft copy.
For disk standardization, some optical disks have characteristic data or a control track recorded thereon as mode data varying for different manufacturers. This control track is recorded in a characteristic data recording area provided inward of a data recording area, the former area serving for recording characteristic data and the latter for recording data. Mode data representing by which manufacturer each optical disk is manufactured, is recorded on the control track in a bar code in conformity with the specification. Each bar of the bar code is formed in a block consisting of a plurality of bits. The control track bears several data about the characteristic of the optical disk, such as the reflection factor of the coating layer, the laser power for data writing, the laser power for data readout and the number of sectors per track, which are all used to determine the read/write mode (specification).
Although provision of the control track is considered, no consideration has been given as to how to accurately read out the recorded data from the control track. This raises a shortcoming such that the control track (characteristic data) cannot be accurately read out from the characteristic data recording area.
Further, according to the optical disk apparatus, to reproduce recorded data from an optical disk, a signal from an optical head is differentiated using an integral circuit consisting of a capacitor and a resistor, the differentiated signal is amplified by an amplifier and the amplified signal is converted into a binary signal by a binary circuit.
With the use of such an optical disk apparatus, however, due to data defect originated from a variation in recorded state of data or the like, the signal from the optical head may have an area where its amplitude is lower than what it should be, and the signal as a whole is likely to swell because of surface fluttering, eccentricity (deformation) or the like of an optical disk. This cannot ensure the signal from the optical head to have a constant level for its stable binary conversion, and cannot therefore achieve accurate data reproduction from the optical disk.
Furthermore, the master plate preformat data recorded on an optical disk at the time the master plate is manufactured is of a different type from that of data which is to be recorded on this optical disk by the aforementioned optical disk apparatus. The preformat data is recorded at the same time recording tracks are provided on the master plate by a stamper and includes address data.
The signals from the optical head which are respectively associated with the preformat data and data recorded on the optical disk have different amplitudes. If the preformat data and the recorded data are subjected to binary conversion with respect to the same detection level, a transient phenomena originating from the difference in amplitude becomes large and a stable reproduction signal may not be attained. This results in unstable binary conversion and inaccurate data reproduction.